[PATCH v2 1/1] virtio: Restore semantics of vq->broken in virtqueues

[Alexander Atanasov]

virtio: harden vring IRQ (8b4ec69d7e09) changed the meaning
of vq->broken which results in vring_interrupt handles IRQs for
broken drivers as IRQ_NONE and not IRQ_HANDLED and made impossible
to initiallize vqs before the driver is ready, i.e. in probe method.
Balloon driver does this and it can not load because it fails in
vqs_init with -EIO.

So instead of changing the original intent ot the flag introduce
a new flag vq->ready which servers the purpose to check of early IRQs
and restore the behaviour of the vq->broken flag.

Acked-by: Jason Wang <jasowang@xxxxxxxxxx>
Signed-off-by: Alexander Atanasov <alexander.atanasov@xxxxxxxxxxxxx>
---
 drivers/virtio/virtio_ring.c  | 33 ++++++++++++++++++---------------
 include/linux/virtio.h        |  4 +++-
 include/linux/virtio_config.h | 12 ++++++------
 3 files changed, 27 insertions(+), 22 deletions(-)

V1->V2: 
  Reworked on top of config option to disable the hardening.
  

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 643ca779fcc6..f0e645e17848 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -100,6 +100,9 @@ struct vring_virtqueue {
 	/* Other side has made a mess, don't try any more. */
 	bool broken;
 
+	/* the queue is ready to handle interrupts */
+	bool ready;
+
 	/* Host supports indirect buffers */
 	bool indirect;
 
@@ -1708,10 +1711,9 @@ static struct virtqueue *vring_create_virtqueue_packed(
 	vq->we_own_ring = true;
 	vq->notify = notify;
 	vq->weak_barriers = weak_barriers;
-#ifdef CONFIG_VIRTIO_HARDEN_NOTIFICATION
-	vq->broken = true;
-#else
 	vq->broken = false;
+#ifdef CONFIG_VIRTIO_HARDEN_NOTIFICATION
+	vq->ready = false;
 #endif
 	vq->last_used_idx = 0 | (1 << VRING_PACKED_EVENT_F_WRAP_CTR);
 	vq->event_triggered = false;
@@ -2157,15 +2159,16 @@ irqreturn_t vring_interrupt(int irq, void *_vq)
 		return IRQ_NONE;
 	}
 
-	if (unlikely(vq->broken)) {
+	if (unlikely(vq->broken))
+		return IRQ_HANDLED;
+
 #ifdef CONFIG_VIRTIO_HARDEN_NOTIFICATION
+	if (unlikely(!vq->ready)) {
 		dev_warn_once(&vq->vq.vdev->dev,
 			      "virtio vring IRQ raised before DRIVER_OK");
 		return IRQ_NONE;
-#else
-		return IRQ_HANDLED;
-#endif
 	}
+#endif
 
 	/* Just a hint for performance: so it's ok that this can be racy! */
 	if (vq->event)
@@ -2207,10 +2210,9 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
 	vq->we_own_ring = false;
 	vq->notify = notify;
 	vq->weak_barriers = weak_barriers;
-#ifdef CONFIG_VIRTIO_HARDEN_NOTIFICATION
-	vq->broken = true;
-#else
 	vq->broken = false;
+#ifdef CONFIG_VIRTIO_HARDEN_NOTIFICATION
+	vq->ready = false;
 #endif
 	vq->last_used_idx = 0;
 	vq->event_triggered = false;
@@ -2429,14 +2431,15 @@ void virtio_break_device(struct virtio_device *dev)
 }
 EXPORT_SYMBOL_GPL(virtio_break_device);
 
+#ifdef CONFIG_VIRTIO_HARDEN_NOTIFICATION
 /*
  * This should allow the device to be used by the driver. You may
  * need to grab appropriate locks to flush the write to
- * vq->broken. This should only be used in some specific case e.g
+ * vq->ready. This should only be used in some specific case e.g
  * (probing and restoring). This function should only be called by the
  * core, not directly by the driver.
  */
-void __virtio_unbreak_device(struct virtio_device *dev)
+void __virtio_device_ready(struct virtio_device *dev)
 {
 	struct virtqueue *_vq;
 
@@ -2444,12 +2447,12 @@ void __virtio_unbreak_device(struct virtio_device *dev)
 	list_for_each_entry(_vq, &dev->vqs, list) {
 		struct vring_virtqueue *vq = to_vvq(_vq);
 
-		/* Pairs with READ_ONCE() in virtqueue_is_broken(). */
-		WRITE_ONCE(vq->broken, false);
+		WRITE_ONCE(vq->ready, true);
 	}
 	spin_unlock(&dev->vqs_list_lock);
 }
-EXPORT_SYMBOL_GPL(__virtio_unbreak_device);
+EXPORT_SYMBOL_GPL(__virtio_device_ready);
+#endif
 
 dma_addr_t virtqueue_get_desc_addr(struct virtqueue *_vq)
 {
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index d8fdf170637c..a63120477ae1 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -131,7 +131,9 @@ void unregister_virtio_device(struct virtio_device *dev);
 bool is_virtio_device(struct device *dev);
 
 void virtio_break_device(struct virtio_device *dev);
-void __virtio_unbreak_device(struct virtio_device *dev);
+#ifdef CONFIG_VIRTIO_HARDEN_NOTIFICATION
+void __virtio_device_ready(struct virtio_device *dev);
+#endif
 
 void virtio_config_changed(struct virtio_device *dev);
 #ifdef CONFIG_PM_SLEEP
diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index b47c2e7ed0ee..472d4703d499 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -260,22 +260,22 @@ void virtio_device_ready(struct virtio_device *dev)
 #ifdef CONFIG_VIRTIO_HARDEN_NOTIFICATION
 	/*
 	 * The virtio_synchronize_cbs() makes sure vring_interrupt()
-	 * will see the driver specific setup if it sees vq->broken
-	 * as false (even if the notifications come before DRIVER_OK).
+	 * will see the driver specific setup if it sees vq->ready
+	 * as true (even if the notifications come before DRIVER_OK).
 	 */
 	virtio_synchronize_cbs(dev);
-	__virtio_unbreak_device(dev);
+	__virtio_device_ready(dev);
 #endif
 	/*
-	 * The transport should ensure the visibility of vq->broken
+	 * The transport should ensure the visibility of vq->ready
 	 * before setting DRIVER_OK. See the comments for the transport
 	 * specific set_status() method.
 	 *
 	 * A well behaved device will only notify a virtqueue after
 	 * DRIVER_OK, this means the device should "see" the coherenct
-	 * memory write that set vq->broken as false which is done by
+	 * memory write that set vq->ready as true which is done by
 	 * the driver when it sees DRIVER_OK, then the following
-	 * driver's vring_interrupt() will see vq->broken as false so
+	 * driver's vring_interrupt() will see vq->ready as true so
 	 * we won't lose any notification.
 	 */
 	dev->config->set_status(dev, status | VIRTIO_CONFIG_S_DRIVER_OK);
-- 
2.25.1